AIR COOLING DESIGN ON STAND PIPE USED FOR CONTROL ROD OF HTTR

One of the problems encountered in the HTTR design was the air cooling design on stand pipe (SP) used for control rod. Control rod drive mec hanism (CRDM) is installed in the control rod SP. If the CRDM temperat ure exceeds 180 degrees C, the CRDM would malfunction because of reduc tion of the electrical insulation. Therefore we studied proper air coo ling method on the control rod SPs by a three-dimensional thermal-hydr aulic analysis. The analytical model was validated by comparing analyt ical results with experimental ones. The flow test was carried out wit h a 1/2 scale model where air flow around the SPs was visualized In an alyses circular cylindrical SPs were modeled simply by rectangular pil lar ones to achieve the equivalent volume. Momentum drop by SP bundle was set for the analyses. Analytical results of air flow around the SP s were in good agreement with experimental ones. Analytical results al so showed that five air outlet nozzles at 30 degrees intervals on ring -duct surrounding the SP bundle are selected as proper design conditio n and the CRDM temperature is well below the limit.